Timepieces with torsion resonators

ABSTRACT

A torsion resonator comprises an elongated torsion bar made in one flat piece with anchor-shaped ends supporting masses and an enlarged median zone at one side of which it is fixed by an elastically deformable branch to the bottom plate of a timepiece. An electrical transducer maintains torsional oscillation of the resonator and the relatively high torsional moment of inertia of the median zone compared to the rest of the bar prevents torsional efforts being transmitted to the supporting branch. Cooperating parts at the ends of the torsion bar and on the plate limit the amplitude of displacement of the torsion bar about the elastic branch.

United States Patent 1191 Kiiffer 1 Jan. 1, 1974 1 TIMEPIECES WITH TORSION 3,316,708 5 1967 Waldburger 58/23 TF RESONATORS 3,599,420 8/1971 Oguey 58/23 V 3.616.636 11 1971 Chopard et al. 58 23 TF Inventor: pp Kuffer, Blenne, tz and 3,628,324 12/1971 Chopard et al. 58/23 D Assignees: Montres Rolex q Geneva; 3,642,344 2/l972 Corker 310/36 X Manufacture Des Montres Rolex FOREIGN PATENTS OR APPLICATIONS Bienne; Societe Anonyme De 1,108,028 3/1968 Great Britain 58/23 TF La Fabrique DHorlogeric Le C lr C Le Sender, Primary Examiner-Richard B. Wilkinson f$W1t Assistant ExaminerStanley J. Witkowski [22] Filed: Sept 20 1971 Att0rr1eyStevens, Davis, Miller & Mosher [21] Appl. No.: 182,085 5 ABSTRACT A. torsion resonator comprises an elongated torsion [30] Foreign Application Priority Data bar made in one flat piece with anchor-shaped ends Sept. 29, 1970 Switzerland 14403 70 Supporting masses and an enlarged median Zone at one side of which it is fixed by an elastically deform- 52 vs. c1. 58/23 v, 310/36 able branch to the bottom plate of a timepiece An 5 Int Cl 04 3 00 G04c 5/00 electrical transducer maintains torsional oscillation of 53 pi f Search M 5 23 TF 23 V 23 the resonator and the relatively high torsional moment 310 3 2 54 of inertia of the median zone compared to the rest of the bar prevents torsional efforts being transmitted to l 5 References Cited the supporting branch. Cooperating parts at the ends UNTED STATES PATENTS of the torsion bar and on the plate limitthe amplitude of displacement of the torsion bar about the elastic R25,3'28 2/l963 Detwllcr et a]. 310/36 X branch 3,595,007 7 1971 Baker 58/23 v 1 3,613,351) 10/1971 Kurino 58/23 TF 5 Claims, 2 Drawing Figures PATENTEDJAN 1 I914 1 TTMEPIECES WITH TORSION RESONATORS The present invention relates'to timepieces with torsion resonators which comprise two masses fixed to the ends of a torsion bar parallel to the plane of a supporting frame, and means for fixing the resonator to the frame.

The fixation means for known torsion resonators is formed by an unilateral or bilateral link attached to the central part of the resonator. A bilateral link, i.e., a link on both sides of the resonator, has the disadvantage of taking up space in a location which should normally be reserved for the gear train and, moreover, produces a hyperstatic coupling sensible to deformation of the bottom plate and unfavourable to frequency stability. An unilateral link, i.e., a link attached to only one side of the resonator, eliminates these drawbacks, but it is observed that if the torsion bar is directly connected to a fixation link formed by a transversal flexion bar, a coupling is produced due to deformation of the torsion bar in the vicinity of the link, which deformation produces a torsional couple about an axis perpendicular to the torsional axis of the torsion bar. lt is thus observed that this coupling produces a loss of energy corresponding to a reduction of the quality factor and above all a socalled systematic support" effect the result of which is a difference of timekeeping of up to several minutes per day between a watch held on a fixed support surface and a watch suspended in the air or carried on a wrist.

According to the invention, there is provided a timepiece comprising in combination a support member defining a supporting plane; a torsion resonator comprising an elongate rectilinear torsion bar having a longitudinal torsional axis, masses fixed at two ends of said bar, and a median zone of said bar having a moment of inertia about said torsional axis substantially greater than the moment of inertia of the rest of said bar about said torsional axis; and fixation means for fixing the resonator to the frame with the resonator substantially parallel to said plane, said fixation means supporting said bar at one side only of said median zone.

By use of this enlarged zone at the junction of the torsion bar and its fixation means which, at first sight, would appear to be only of minor importance, the reaction of the fixation means is diminished by a degree such that its effect on timekeeping can be reduced to less than one second per day. Moreover, the quality factor of the resonator is improved, and is independent of the manner in which the watch, for example, is worn.

The accompanying drawings show, by way of example, an embodiment of a timepiece according to the invention.

FIG. 1 is a schematic plan view of this timepiece;

FlGsZ is an enlarged scale cross-section along line 2-2 of FIG. 1.

The timepiece shown in FIG. 1 comprises a bottom plate 1 on which a torsion resonator is fixed parallel to the plane of the plate by a T-shaped fixation foot 2, the branch 3 of which forms an elastic liason element connecting the transversal bar of the T to an enlarged median part 4 of a torsion bar 5.

Each end of the torsion bar 5 terminates with two arms 6, 6' substantially in the form of an anchor. The arms located on one side of the torsional axis of the bar 5 of the resonator each carry a magnetic pot 7, 7' forming part of an electrodynamic transducer and the arms located on the other side of this torsional axis each carry counter-weights 8, 8'. Each mass 6, 7, 8 and 6', 7', 8 is arranged so that its center of gravity and one of its principal axes of inertia are located along the torsional axis of the torsion bar 5.

The torsion bar 5, the T-shaped fixation foot 2 and the anchor-shaped ends of the torsion bar have a uniform thickness and are made in a single piece by stamping. The magnetic pots 7, 7' and the counter-weights 8, 8' can be rigidly fixed to the resonator by pinning, screwing, welding or sticking and in this example, the magnetic pots are fixed to the resonator by screws 9, 9'.

The anchor-shaped ends of the torsion bar 5 ensure that the magnetic pots 7, 7 and the counter-weights 8, 8' are located close to a diameter of the plate 1 perpendicular to the torsional axis of the bar 5. This disposition enables the use of a single maintenance coil 10 common to the two magnetic pots 7, 7' and the location of a supply battery 11 between the two counterweights 8, 8.

Each magnetic pot 7, 7 comprises two permanent magnets 12, l3, 12, 13' respectively and a soft-iron piece 14, 14 forming a magnetic circuit. Two pieces l5, l6, 15, 16 in brass or heavy metal increase the mass of each pot. The coil 10 is held in place by a body 17 with a central cavity 18 which can house electrical components (not shown) of a maintenance circuit, such as transistors, resistors, and capacitors, in the form of separate or integrated elements, connected to the coil 10 and to the supply battery 11. The flux of the permanent magnets 12, 13, 12', 13' is concentrated in the vicinity of the coil 10 by means of the magnetic circuits formed by pieces 14 and 14. The residual magnetization of the magnets produces a field in the direction indicated by arrows F in the region between the polar faces. If, at a given moment, a current is passed through the coil 10 in the direction indicated by arrow F,, the magnets are acted upon by forces in the directions indicated by arrows F and F The frequency of the current feeding the coil 10 is chosen to coincide with the natural frequency of the resonator, which enables maintenance of the oscillations of the resonator, these oscillations involving a substantially vertical movement of the pots 7, 7 in opposite phase.

The transformation of the oscillations of the resonator into a rotational movement is obtained by means of a pawl and ratchet device comprising a driving pawl 19 fixed to the counter-weight 8' and the free end of which engages with the teeth of a ratchet wheel 20. Thepoint of operation-of the driving pawl 19 carries a stone 22 located, seen in plan, approximately mid-way between the point of fixation of the torsion bar 5 and one of its free ends and over the torsional axis or neutral line of the torsion bar 5, but above the plane of the resonator so as to provide a sufficient amplitude of the stone 22. The stone 22 moves along an arc, the center of rotation of which is the torsional axis of the bar 5; only the component parallel to the plane of the plate 1 is used to drive the ratchet wheel 20, the component perpendicular to the plate 1 causing friction between the stone 22 of the driving pawl 19 and the teeth of the ratchet wheel 20. However, this friction can be considered as negligible.

A retaining pawl 21 is fixed on a small plate 23 pivotally mounted about the axis of the ratchet wheel 20 and angularly adjustable by means of an eccentric pin 24. By turning the eccentric pin 24, the phase between the pawls 19 and 21 can be modified without changing the pressure of the retaining pawl 21 on the ratchet wheel 20.

The ratchet wheel 20 meshes with a schematically shown reducing gear train including a wheel 25 located at the center of the plate 1. The wheel 25 may carry a seconds hand (not shown) on a central shaft. To allow room for this wheel 25, the torsion bar 5 is located parallel to and fairly close to a diameter across the substantially circular plate 1, the fixation foot 2 being located on the side of the torsion bar furthest away from this diameter.

Two pins 26, 26' respectively protrude from the ends of the torsion bar 5 coaxially to its torsional axis. These pins 26, 26' freely pass through two circular apertures 27, 27 concentric to the torsional axis provided in two small plates 28, 28 fixed on the edge of the plate 1 by means of feet and a screw (not shown). The radial play between the pins 26, 26' and the edge of the respective apertures 27, 27 is about 0.05mm, which enables limitation of undesired movements of the resonator caused by vibrations or by accelerations to which the timepiece is subjected. ln view of the fact that the limitation means (pins and apertures) are centred on the torsional axis of the torsion bar 5, friction between the edges of the openings and the pins is reduced to a minimum.

The point to point angular amplitude of the pins 26, 26 is about 1. Parts of the circumferences of the limitation pins can thus only have a very small movement and, in the case of mechanical contact between the pins and the small plates, friction is very low. Because of this, absorbtion of the operating amplitude of the resonator is minimal. The described limitation means come into operation for any acceleration or vibration of the resonator perpendicular to the torsional axis.

The limitation means can be mounted anywhere on the torsion bar. However, mounting at the end of the bar, as described, facilitates observation of the radial play between the pins 26, 26 and the apertures 27, 27' in the small plates 28, 28'. Of course, the pins could be integral with the small plates while the openings could be provided in the ends of the torsion bar 5.

When the resonator oscillates, its two anchor-shaped ends 6, 6' oscillate about the torsional axis of the torsion bar 5 in opposite phase. This oscillation of the resonator is maintained by the transducer formed of the magnetic pots 7, 7, the coil 10 and the maintenance circuit in the central cavity 18 of the body 17, as previously described. The enlarged median part 4 of the torsion bar 5 enables diminution of the coupling between the resonator and the plate 1. The polar moment of inertia of the part 4 is about fifty times greater than the moment of inertia of the elastic part of the torsion bar 5. The median part 4 undergoes virtually no deformation when the resonator oscillates and in this manner the T-shaped fixation foot 2 is not deformed and does not transmit energy to the plate 1. The reaction of the support is thus strongly diminished which considerably increases the precision of the timepiece.

The elastic liason provided by the bar 3 of the fixation foot 2 and the thickened median part 4 of the torsion bar 5 enables reduction of the disequilibrium effect of the resonator. The purpose of this elastic liason is to absorb the effect of any slight asymmetry between the two parts of the resonator.

What is claimed is:

1. A timepiece comprising in combination a support member defining a supporting plane; a torsion resonator comprising an elongate rectilinear torsion bar having a longitudinal torsional axis, masses fixed at two ends of said bar, and a median zone of said bar having a moment of inertia about said torsional axis substantially greater than the moment of inertia of the rest of said bar about said torsional axis; and fixation means for fixing the resonator to the support member with the resonator substantially parallel to said plane, said fixation means supporting said bar at one side only of said median zone.

2. A timepiece as claimed in claim 1, in which said torsion bar including said median zone, and said fixation means are made in a single flat piece of uniform thickness obtained by stamping.

3. A time piece as claimed in claim 1, in which said support member is substantially circular, said torsion bar being fixed parallel to and in the vicinity of a diameter across siad support member, said fixation means being located on the side of the torsion bar furthest away from said diameter.

4. A timepiece as claimed in claim 3, in which said fixation means comprises a first part substantially parallel to said torsion bar, means for fixing said first part to said support member, and an elastically deformable second part joining said median zone to said first part.

5. A timepiece as claimed in claim 4, in which at least one part of said resonator and at least one cooperating part of said support member together form means for limiting flexion of said torsion bar about said fixation means. 

1. A timepiece comprising in combination a support member defining a supporting plane; a torsion resonator comprising an elongate rectilinear torsion bar having a longitudinal torsional axis, masses fixed at two ends of said bar, and a median zone of said bar having a moment of inertia about said torsional axis substantially greater than the moment of inertia of the rest of said bar about said torsional axis; and fixation means for fixing the resonator to the support member with the resonator substantially parallel to said plane, said fixation means supporting said bar at one side only of said median zone.
 2. A timepiece as claimed in claim 1, in which said torsion bar including said median zone, and said fixation means are made in a single flat piece of uniform thickness obtained by stamping.
 3. A time piece as claimed in claim 1, in which said support member is substantially circular, said torsion bar being fixed parallel to and in the vicinity of a diameter across said support member, said fixation means being located on the side of the torsion bar furthest away from said diameter.
 4. A timepiece as claimed in claim 3, in which said fixation means comprises a first part substantially parallel to said torsion bar, means for fixing said first part to said support member, and an elastically deformable second part joining said median zone to said first part.
 5. A timepiece as claimed in claim 4, in which at least one part of said resonator and at least one cooperating part of said support member together form means for limiting flexion of said torsion bar about said fixation means. 